Liquid development of electrostatic latent images



April 2; 1963 R. w. GUNDLACH 3,

LIQUID DEVELOPMENT OF ELECTROSTATIC LATENT IMAGES Filed May 7, 1959 INVENTOR. Robert W. Gundlach A 7' TORNE Y .fitte ice 3,ll4,43 LllQlUllD DEVELUEMENT G l ELEfiTRQdTATIC LATENT EMA-GEES This invention relates in general to electrostatic recording and, in particular, to image development in the art of xerography.

In electrostatic recording as typified by xerography, it is usual to form an electrostatic image on an insulating or photoconductive insulating surface, generally conforming to information to be recorded or reproduced. This image may then be developed or made visible by the application of an elcctrostatically attractable material which deposits in conformity with the electric image to produce a visible record. In the usual embodiments of xerographic development it is conventional to employ finely divided insulating materials, gener lly powders, which are presented to the image bearing surface in particulate form. Thus, commercially, the electric image is generally developed by cascading across the image surface a mixture of relatively large beads or granules bearing on their surfaces finely divided pigmented insulating dust particles. Alternatively, insulating or conductive dust or liquid ink have been presented to the image in an air sus pension. Likewise, developer dust may be carried on the surface of a brush or brush-like fiber such as a fur brush or a simulated brush of magnetically adhering particles.

Now in accordance with the present invention, an electrostatic latent image is developed or made visible by presenting to the image surface a liquid or ink developer on the surface of a suitable developer dispensing member. In this new development operation it has been found that the apparatus and method produce essentially pure black or colored image areas on absolutely plain or white background areas. Further, it has been found that apparatus in accordance with this invention is new and simplified when compared with previously developing devices.

In addition, in accordance with this invention, images are developed simultaneously with exposure, thus providing the developed image more rapidly than has generally been possible heretofore. Again, quality is excellent.

A further understanding of the invention will be presented in the following specification and in the drawings in which:

HG. 1 is a diagrammatic view of a developer dispensing member according to one embodiment of the invention;

PEG. 2 is a cut away enlarged diagrammatic View of the developer dispensing member applying developer to an image bearing surface;

FIG. 3 is an enlarged diagrammatic view of simultaneous development with exposure.

FIG. 4 is a diagrammatic illustration of a xerographic machine according to an embodiment of the invention.

Referring now to PEG. 1, there is illustrated a developer dispensing member 12 which comprises a support base it) having disposed on its surface a raised pattern 11 which may, for example, comprise a plurality of hue raised lines, dots, or other raised material. This member is characterized by being wettable in the depressions or valleys formed by the raised areas ll by the developer employed, but substantially non-wettable along the peaks. This is accomplished, for example, through the use of a support base 10, such as a sheet or web, having a relatively uniform surface comprising a material that is easily wettable by the developer being used. When the developer comprises an aqueous base material, then the surface of support base It? may comprise a hydrophilic surface and the pattern or raised areas 11 may comprise hydrophobic material positioned on the hydrophilic surface. Alternatively, a pattern of hydrophilic dots or discs carrying a deposit of hydrophobic material thereon may be posrtioned on substantially any surface. Other composites which will readily occur to those skilled in the art are also intended to be included herein. Preferably, when employing water base inks as the developer, the surface of the support base is hydrophilic and thus may comprise a master plate or mat as is conventionally used in the art of lithography. A highly satisfactory support base includes a zinc, aluminum, or paper base lithographic plate conventionally used as an image master in lithography. Likewise, other metal, plastic or paper surfaces may be employed, preferably with a coating treatment or other surface treatment to render the surface hydrophilic. If an oil base developer such as an oil base ink is to be employed, it is desirable that the support base or the valleys or depressions be a hydrophobic or oil wet-table surface. Most resin surfaces are receptive to oil base inks and thus may be used. In addition, if a surface coating is desired, it has been found that a rosin modified phenol formaldehyde resin is a conveniently workable material capable of being coated in a thin layer on most surfaces and characterized by good receptivity to oil base ink.

The patterned material on the developer dispensing surface should be a very finely divided pattern, desirably regular in configuration or at least in pattern size, and adapted to maintain spacing between a developer dis pensing surface and a developer receiving surface sufficient to keep the developer out of contact with the image surface in the background areas.

A finely divided raised pattern 11 may be placed on the support base ill by any desired means. For example, a photoresist coating may be formed in a fine half-tone pattern by conventional photographic means to provide a pattern on the support base surface consisting of a plurality of half-tone dots or a pattern of fine lines. 'lenorally, a pattern of dots is preferred over pattern of lines so that the developer receiving valleys rather than the peaks will be the continuous surface. The presently preferred method of forming the pattern is to produce a resin pattern in half-tone dots by xerographic means in which, for example, a commercial xerographic plate may be charged and exposed to light projected through a halftone screen and the resulting electrostatic image may be conventionally developed to produce a half-tone dust pat tern. This pattern is then transferred to the support base and is fused to provide a permanently adhering raised pattern on the support base surface. The dot pattern should be relatively fine, generally at least a 6(l-line screen and preferably between about a 180 and about a BOO-line screen. A suitable dot pattern can be formed by xerographic means as, for example, by exposing a commercial xerographic plate to a ZQO-line screen pattern, developing the plate in the usual manner and transferring the developed image and fusing it onto a zinc lithographic plate. In the fused half-tone pattern the dots or lines of fused material are about preferably 50 microns in height and generally between about 5 microns and microns high.

The thus-prepared developer dispensing member is pre pared for use by an inking process in which ink is supplied to fill the valleys between the islands or dots of the pattern. This may be accomplished, for example, by wiping the surface with a thoroughly inked cloth or by means of inking rolls or the like, preferably followed by squeegeeing off the excess ink. When prepared in this manner, the developer dispensing member bears on its surface a substantially uniform film of developer punctured by the dots or other raised pattern in such a manner that a smooth surface pressed in contact with the developer dispensing member is in contact only with the non-inked peaks of the pattern and not with the developer film. Desirably, suliicient ink should be placed on and allowed to remain on the surface of the developer dispensing member so that this member may be placed against a sheet of paper or other relatively smooth surface without transferring quantities of developer to such surface.

In FIG. 2 is illustrated the mechanism of an embodiment of electrostatic development employing the developer dispensing member 12 illustrated in FIG. 1. In this figure is shown a xerographic plate 13 comprising, for example, a support base 14 having on its surface an insulating or photoconductive insulating layer 15 such as, for example, a vitreous or amorphous selenium coating on a metal base as is well known in the art of xerography. An electrostatic image to berecorded is placed on the xerographic plate by means of application of electric field and exposure to activating radiation as, for example, by charging the plate surface preferably to positive polarity and exposing to a light image to be recorded. Charge dissipation in the light-struck areas results in a positive polarity electrostatic image corresponding to the dark areas of the light image. Alternatively, non-optical image forming means may be employed, and charges may be deposited on non-light sensitive insulating layer-s.

The xerographic plate 13 hearing a charge pattern as indicated by the plus marks 17 is brought into contact with the developer dispensing member, with the selenium or other insulating surface 15 pressing against the dots 11 on the developer dispensing member 12. As illustrated, base 16 is connected through variable potentiometer 16 across battery 18, and support base 14 of plate 13 is grounded. Base is grounded in this illustration.

In areas where there is electric charge on the xerogra-phic plate surface, developer creeps up the sides of the dots 11 into contact with the xerographic plate. In the background or non-image areas the developer does not creep up the dots and those areas of the plate remain out of contact with the developer layer. Thus, developer reaches the plate only in image areas. For image development the surface of the developer dispensing member is pressed either simultaneously or progressively into contact with the area in which a pattern is to be developed onthe image bearing surface, causing developer transfer to the image surface in conformity with the electrostatic image. When dealing with ridged surfaces where the ridges are coextensive with one another and the developer material is not all in flowing contact, then it has been found desirable to place or move the ridged material relative to the surface being developed in at least two directions during two passes or developments to cause high quality development. However, a single positioning or pass in one direction gives adequate quality for many applications.

In FIG. 3 is illustrated an embodiment of simultaneous development with exposure in accordance with this invention. As in FIG. 2, plate 13 comprising photoconductive insulating layer overlying backing member 14 is positioned against developer dispensing member 12 with the surface of photoconductive insulating layer 15 pressing against dots ill on support surface 10. Support surface 10' of developing dispensing member 12 is connected through potentiometer 16 across battery 18 to a raised positive potential, and backing member 14 of plate 13 is grounded. In this embodiment backing member 14 of plate 13 is light transparent and may comprise, for example, NESA glass. Directed through transparent backing 14 and to the photoconductive insulating layer is a pattern of light and shadow. In this figure a lighted area 19 is shown for illustrative purposes to illustrate the light of the light and shadow pattern directed to the photoconductive insulating layer 15. The effect of lighted area 19' on plate 13 is to cause charge dissipation in the areas being struck by light illustrated in this figure as a merging of positive and negative polarity charges within photoconductive insulating layer 15 in the area of exposure. In these same exposed areas ink creeps up the sides of dots 11 and into contact with the xerographic plate. In the areas not exposed the developer does not creep up dots 11 and those areas of plate 13 remain out of contact with the developer material. Thus, developer reaches the plate only in areas being exposed in accordance with this embodiment. Following exposure, the light image is removed from plate 13 and plate 13 is separated from developer dispensing member 12 leaving on the surface of plate 13 a developed image conforming in configura-- tion to the exposure pattern to which plate 13 has been: exposed.

In FIG. 4 is illustrated a xerographic machine incorporating one embodiment of the present invention. This machine is a continuously operating xerographic machine employing a rotatable cylinder operating on a principle that is employed in commercially available Copyilo machines, available from Haloid Xerox Inc., Rochester, New York. As illustrated, the xerographic drum, generally designated 20, is rotatably mounted so as to move past a series of xerographic stations for image formation. The drum includes generally a metal or other electrically conductive support member coated with a photoconductive insulator such as a layer of vitreous or amorphous selenium or a layer of a photoconductive pigment in a suitable insulating binder. Positioned around the xerographic drum is a charging electrode 21 such as, for example, a high voltage corona discharge electrode adapted to supply ions or electric charges to the xerographic drum surface. At an exposure station, generally designated 22, an image to be reproduced is projected onto the drum surface by means of a lens 23 desirably operating in conjunction with slit exposure mechanisms (not shown) synchronized to the motion of the drum.

At a development station, generally designated 24, is a continuous development mechanism operating in accordance with the illustration of FIG. 2 as will be described more completely hereinafter. 7 At this development station the electrostatic latent image on the xero? graphic drum is developed or made visible by deposition of developer thereon.

Next in the direction of rotation following development station 24 is a transfer station, generally designated 25, at which a suitable transfer web 26 such as a web of paper or the like is fed from a supply roll 27 to a take-up roll 28 passing between the xerographic drum 2!): and a transfer roller 29. Inasmuch as development according to the present invention generally contemplates the use of liquid ink, transfer by means of pressure alone is generally satisfactory, although it is to be understood that additional transfer means such as electric fields may be employed if desired. The surface of the drum then moves past an optional cleaning station, generally designated 20, where residual developer material, if any, may be removed from the drum surface to prepare the drum for recycling past the xerographic operational stations.

At development station 24 is positioned mechanism for development in accordance with one embodiment of the present invention. Suitably mounted to bear against the xerographic drum 2t) and to move simultaneously with the surface of the drum is a developer dispensing belt or webfrS. This web in general comprises an endless web or belt developer dispensing member such as illustrated in FIG. 2 and includes, for example, an ink receptive support base bearing a raised pattern of ink repellent spacing material as illustrated in FIG. 1. A suitable series of guide rolls 36 gude the web in a continuous path into contact with the xerographic drum surface and into an inking station, generally designated 37 At inking station 37 a suitable ink supplying means serves to apply marking material or ink to the surface of developer dispensing web 35. The ink supplying means optionally may include inking rollers 33, loading at an ink source 42. Desirably, a wiper 39 mounted on a support 40 is positioned to bear against the developer dispensing web disposed between the inking station 37 and xerographic drum so as to remove excess ink from dispensing web after loading and prior to its use in development. Alternatively, endless web 35 may be omitted and the surface characteristics of this member may be incorporated into a roller, as for example, roller 33 illustrated contacting web 35, and this roller may be positioned to contact the surface to be developed.

In use and operation an electrostatic latent image is placed on the xerographic drum, for example, by charging the drum surface and exposing it to a light image to be reproduced. The image bearing drum surface then moves into the development station where it is contacted with developer dispensing web 35 to deposit ink on the drum in the image areas as illustrated in connection with FIGS. 1 and 2. The inked xerographic drum surface then moves to the transfer station to transfer the image to the print receiving Web to form the final xerographic print. If desired, fusing or drying means may be employed to fix or harden the image on the print support web. The xerographic drum then moves to the cleaning station 3% for preparation for a new cycle of operation.

The ink or developer material used in connection with this invention should be homogeneous and at least so to the extent of the minimum ink deposited. It should also be of a relatively low viscosity, relatively non-volatile, contrasting in color in the usual case to the surface on which it will remain and relatively electrically conductive. It is presently believed that conductivity in both the dispensing member and in the ink or developer is a crtical requirement for operation of this invention. The level of conductivity, however, is not limited to only the very conductive. Instead, it relates to the level of resistivity of the insulating member bearing the image being developed. Generally, it may be'stated that the resistivity of the ink or developer as well as of the support base of the ink dispensing member should be at least three and preferably at least five to six orders of magnitude less resistive or more conductive than the insulating image bearing member. Stated in specific figures, it is preferred that the resistivity of these elements be less than 10 ohm-centimeters and such a resistivity in this invention is considered electrically conductive.

It has been found that the developer deposits not by physical emission from the surface of the developer dispensing member, but instead by creeping up the sides of the pattern material and migrating to the facing image receiving surface. It is presently believed and understood that the mechanism of developer mi ration employs in cooperation the two forces of electrostatic attraction and surface tension in that surface tension retains the developer in cohesive configuration on the surface of the developer dispensing member while electrostatic attraction applies forces causing developer to creep up the sides of the patterned spacing material and transfer only in accordance with the pattern of electric charge. Thus, the developer remains in the valleys of the developer dispensing surface except under the influence of the attracting electrostatic force.

To accomplish development through electrostatic attraction of the developer material on the developer dispensing member to the image bearing surface in image configuration, the support base of the ink dispensing member should be biased (including ground) through connection to a potential source. When so electrically connected the image charges on the surface to be developed induce, due to conductivity through the support base and into the conductive ink, charges which tend to neutralize charges on the surface of the image bearing layer. Thus, as illustrated in FIG. 2, when the support base is grounded and areas of the plate carry positive charges, negative charge is induced through the support base into the liquid developer in those areas positioned adjacent to the positive charges, thus causing a field between the developer and the charge on the surface to be developed in such regions. In areas of ink corresponding to areas of the image bearing surface of FIG. 2 bearing no charge, no attractive field exists to cause charge to migrate into the conductive ink through the support base while the support base is grounded, and accordingly, no electric field of attraction is created to cause ink to creep up the raised areas of the developer dispensing member and to the surface bearing the charge pattern. Thus, as illustrated in FIG. 2, development takes place only in charged areas when the support base is connected to ground or connected to a low potential generally about the level of the uncharged or substantially uncharged areas of the image bearing surface. It is interesting to note that development in accordance with this invention is not polarity sensitive. Thus, development in FIG. 2 does take place as illustrated in the sense that charged areas develop and uncharged areas do not develop if the charged areas are negative in polarity just as development takes place when the charges are positive in polarity as shown. In such a case positive charges would be induced into the ink in areas corresponding to the negative charges on the electrostatic image bearing surface. A field would then exist to cause the ink to creep up the raised area for deposition on the image bearing surface.

In FIG. 2 there is illustrated development of the charged areas. However, if desired, uncharged areas may be developed by applying to the support base a potential of the same polarity and of the same amount as the charged areas on the electrostatic image bearing surface as through a change in the potential applied by varying the potentiometer. In such an instance a field would -xist between areas uncharged on the electrostatic image bearing surface and the developer on the developer dispensing member, and no field would exist in areas of charge and corresponding ink on the developer dispensing member. Thus, in areas of charge there would be no attraction for ink and none would creep up and deposit on the electrostatic latent image bearing surface. However, in areas of no charge charges would be induced to the ink resulting in electric fields of force which would cause ink to deposit on the electrostatic image bearing surface resulting in image development of uncharged areas.

The analysis of operation applied to FIG. 2 is pertinent also to FIG. 3. In this figure the developer dispensing member is biased to the level of charge on the surface being exposed. As an area discharges due to light exposure electric fields of force come into being between the light sensitive member and the ink on the developer dispensing member. There follows induction of charge into ink in this area and the creation of electric fields of force between the ink and the surface in the area being 7 during sensitization. Also, one can accomplish development in areas not exposed by applying to the support base of the developer dispensing member a varying potential controlled by the light decay characteristics of the photoconductive insulating layer being exposed. By so doing the potential applied to the developer dispensing member maintains a no field condition betweenthis member and the surface being exposed in areas being exposed during exposure; whereas in areasnot exposed a field develops as exposure continues and ink deposition takes place correspondingon the non-exposed areas.

In practice it has been found that it is generally desirable to apply a slight bias to overcome the reluctance of the develoyer material to transfer to the plate and to assure highquality and background-free developer deposition on the charge pattern bearing surface. Thus, when applying a raised potential to the developing dispensing member, it is desirable to add about another 50 volts so that if areas of the plate are at a. level of 450 volts the developing dispensing member will have applied approximately 500 volts to result in ink deposition in areas which have been discharged on the surface being developed. This additional potential applied to the developer dispensing member creates a stronger field for liquid movement and deposition. Similarly, when developing charged areas and-brackground areas are at about a raised potential of volts positive it is desirable'to apply apotential of approximately 30 to 50 volts negative to the developer dispensing member.

The surface tension of the ink or developer is not presently believed to be critical. When dealing with an extreme surface tension, one compensates for this condition. Thus, when using a material of very low surface tension, it is preferred that the surface to be developed be placed above the ink dispensing member to cause ink flow in an upward direction and in a direction opposite to the direction of pull by gravity. A larger peak may also be used where a material of extremely low surface tension is being employed. When the material has a high surface tension, then lower peaks as well as development including flow in the direction of gravity is helpful. An additional aid is to use a bias on the support surface to aid developer movement to the surfacebeing developed. Thus, it is sometimes desirable to place a potential of 200 or even 300 volts on the developer dispensing member where development of uncharged areas is desired and where the low potential on the surface being developed is in the order of to volts.

Of the'various materials tested in connection with this invention, bestresults have been had with commercially available inks. These generally comprise either a water or oil soluble dye dissolved in water or oil depending on the dye. They also include alcohol base inks as well as these various base inks including additives. For example, to the water base ink there has been added ethylene glycol which reduced the rate of evaporation of the ink. 'Alcohol has been added to a water base ink to obtain a higher concentration of dye. into solution. The variousdevelopers which have been most successfulin connection with this invention have had a surface tension in the range of 15 to 90 dynes/cm.

Although the automatic machine illustrated in FIG. 4 shows the developing system described in connection with FIG. 2, it is to be realized that through minor modifications the developing system illustrated in FIG. 3 which results in development simultaneous with exposure may be embodied into such a machine. This may be accomplished by using a cylindrical drum, as illustrated, having a-transparent backing. The light pattern of exposure is then fed from within the cylindrical drum and through the backing to the light sensitive photoconductive insulating material at the point of the development station of the drum resulting in immediate development. The machine may also be modified by coating the inner surface with photoconductive material and providing a transparent outer layer. In such case exposure may take place as illustrated in FIG. 4, but the developing mechanism is then moved to the internal area of the drum to develop at the point of exposure.

As should also be readily apparent, although in FIG. 4 there is illustrated a cylindrical drum in an automatic machine, flatplates wellknown to xerography, may also be used'and may be transported from station to station to accomplish automatic print production. Such fiat plates may be flexible or rigid and apparatus readily apparent to those skilled in the art is intended to be Within the scope of this invention.

The developed image is utilized in the apparatus of FIG. 4 through transfer to an ink receiving medium. However, as is now known in the art, this image maybe used as a subject to be photographed or as a subject to be projected in one way or another for viewing purposes.

Although throughout emphasis has been on applying a potential to the developer dispensing member, it is to be realized that a potential may be applied by maintaining this member electrically floating. If electrically floating,

when brought to the surface to be developed, the developer dispensing member will become raised in potential to a level equal to the average potential across the surface to be developed. Thus, if developing a surface comprising charge at a level of about 500 volts, the developer dispensing member will "assume a level of about 450 volts. This will readily cause deposition in uncharged areas. However, at the same time, since a potential difference exists between charged areas and the developer dispensing member, some ink deposition can be expected in the charged areas which in the ultimate print are background areas. Accordingly, it is preferred that a controlled potential be applied to the developer dispensing member. However, this is not essential to operation, since a potential may be applied through other means.

Although this invention has been'described in terms of an ink dispensing member comprising wettable valleys and non wettable peaks, it has also [been found that the development methods and apparatus of the present inven tion may be employed in conjunction with homogeneous roughened, grained, or finely patterned surfaces characterized :by rigorous conformity with a finely divided pattern of raised and depressed areas. found possible to employ a grained metal lithographic master in the absence of additionally deposited patterned material. When using such a master surface as the ink or developer dispensing member, the upper surface of the master must be carefully wiped to remove excess ink. When the surface is so cleaned, it has been found that excellent image development can be achieved according to the methods and apparatus of this'invention.

While various embodiments of the present invention have been described and various uses of the present invention have been described, as should readily be apparent, many other applications and variations exist and it is not desired to be limited only to the particular embodimentsand applications described herein, but it is intendedto cover the invention broadly within the spirit and scope ofthe appended claims.

What-is claimed is:

1. The new use of a solid member including a multiplicity of raised portions defining a smooth surface and a plurality of portions depressed below said raised portions in developing xerographic images, comprising covering only said depressed portions with a layer ofconductive liquid ink comprising a homogeneous liquid solution and placingtheraised portions of said member into contact with an electrostatic latent image bearing surface to develop the image.

2. A new use of a solid member including a multiplicity of raised portions defining a substantially regular pattern surface and a plurality of portions impressed below said raised portions in developing electrostatic images, said new use comprising covering only said depressed portions with a layer of conductive liquid ink comprising ahomogeneous liquid solution, placing the raised portions of said member into contact with an electrostatic latent image bearing member, and applying a bias potential to said conductive ink to thereby develop said latent image.

3. In a system of xerography in which an electrostatic Thus, it has been image isdeveloped with liquid ink the improvement comprising loading a developer dispensing member by wetting said member with an electrically conductive ink comprising a homogeneous liquid solution below a surface thereof, said surface comprising substantially regularly dispersed and substantially evenly distributed peaks extending out of said member, placing said peaked surface into physical contact with said electrostatic latent image, and applying an electric bias to said liquid ink to thereby develop said electrostatic image.

4. A method of development in xerogr aphy comprising positioning close but spaced from an electrostatic latent image on an image bearing surface a substantially continuous film of electrically conductive ink comprising a homogeneous liquid solution, providing flow aiding elements in physical contact between said ink and said image bearing surface, and applying a bias to said ink whereby ink moves along said flow aiding elements and develops said electrostatic latent image.

5. The method of image development in xerography comprising positioning close but spaced from an electrostatic latent image on an image bearing surface a developer supply of electrically conductive ink comprising a homogeneous liquid solution, providing between said supply and said image bearing surface flow aiding elements in physical contact With said ink and said image bearing surface, said flow aiding elements being regularly dispersed and substantially evenly distributed throughout the area of contact, and applying to said ink an electrical bias potential to move ink along said flow aiding elements to said image bearing surface in image configuration.

6. The method of claim in which said flow aiding elements are characterized as being substantially nonwettatble by said ink.

7. The method of image development in xerography comprising positioning close but spaced from an electrostatic latent image on an image bearing surface a developer supply of electrically conductive ink comprising a homogeneous liquid solution, providing between said supply and said image bearing surface flow aiding elements in physical contact with said ink and said image bearing surface, said flow aiding elements being regularly dispersed and substantially evenly distributed throughout the area of contact, and applying to said ink an electrical bias potential of substantially ground to move ink along said flow aiding elements to said image bearing surface in areas of charge on said image bearing surface whereby ink is deposited in areas of charge on said image bearing surface.

8. The method of image development in xerography comprising positioning close but spaced from an electrostatic latent image on an image bearing surface a developer supply of electrically conductive ink comprising a homogeneous liquid solution, providing between said supply and said image bearing surface flow aiding elements in physical contact With said ink and said image bearing surface, said flow aiding elements being regularly dispersed and substantially evenly distributed throughout the area of contact, and applying to said ink an electrical bias potential of the same polarity as the charges on the surface to be developed and about equal in potential to the potential of charged areas on the image bearing surface to move ink along said flow aiding elements to said image bearing surface and deposit ink on said image bearing surface in areas of substantially no charge on said image bearing surface.

9. The method of image development in xerography comprising positioning close but spaced from an electrostatic latent image on an image bearing surface a developer supply of electrically conductive ink comprising a homogeneous liquid solution, said ink being positioned on a conductive surface characterized by its ability to wet with said ink, providing between said wettable surface and said image bearing surface flow aiding elements in physical contact with said image bearing surface and said wettable surface, said how aiding elements being characterized as being substantially non-wettable by said ink' and being regularly dispersed and substantially evenly distributed throughout the area of contact, applying to said Wetta'ble conductive surface an electrical bias potential to move ink along said flow aiding elements to said image bearing surface in image configuration, and removing said image bearing surface out of contact with said fiow aiding elements whereby an image is developed in conformance with said electrostatic latent image on said image bearing surface.

10. The method of claim 9 in which said bias potential is about ground and in which ink deposits on said image bearing surface in areas of charge.

11. The method of claim 9 in which said bias potential is of the same polarity as the charges on the surface to be developed and about equal in potential to the potential of charged areas on the image bearing surface thereby causing ink deposition on areas of substantially no charge on said image bearing surface.

12. The method of simultaneously developing during exposure in xerography comprising positioning close but spaced from a uniformly charged surface of a photoconductive insulating layer a developer supply of electrically conductive ink comprising a homogeneous liquid solution at a raised electrical bias potential of the same polarity as the charges on the sensitive photoconductiye insulating surface and at a potential about equal to the potential of the charged photoconductive surface, providing between said supply and said charged photoconductive surface flow aiding elements in physical contact with said ink and said charged surface, said flow adding elements being fine, regularly dispersed and substantially evenly distributed throughout the area of contact, and exposing said photoconductive insulating layer to an image pattern to be reproduced causing ink deposition on the surface of said photoconductive insulating layer in areas of the photoconductor activated during exposure.

13. The method of simultaneously developing during exposure in xerography comprising positioning close but spaced from a uniformly charged surface of a photoconductive insu ating layer on a transparent backing a developer supply of electrically conductive ink comprising a homogeneous liquid solution at a raised electrical bias potential of the same polarity as the charges on the sensitive photoconductive insulating surface and at a potential about equal to the potential of the charged photoconductive surface, providing between said supply and said charged photoconductive surface flow aiding elements in physical contact with said ink and said charged surface, said flow aiding elements being regularly dispersed and substantially evenly distributed throughout the area of contact, and exposing said photoconductive insulating layer through its transparent backing to a light image to be reproduced causing ink deposition on the surface of said photoconductive insulating layer in areas being exposed to light.

14. The method of simultaneously developing during exposure in xerography comprising positioning close but spaced from a uniformly charged surface of a photoconductive insulating layer on a transparent backing a developer supply of electrically conductive ink comprising a homogeneous liquid solution at a raised electrical bias potential of the same polarity as the charges on the sensi tive photoconductive insulating layer and at a potential about equal to the potential of the charged protoconductive surface, providing between said supply and said charged, photoconductive surface flow aiding elements in physical contact with said ink and said charged surface, said flow aiding elements being regularly dispersed and substantially evenly distributed throughout the area of contact, exposing said photoconductive insulating layer through its transparent backing to a light image to be reproduced, and during exposure varying the potential applied to the ink to cause the bias applied to the ink to spa 15043 1 1' remain aboult'equal to the level of charge in the photoconductor at points of light exposure causing ink deposition on the surface of said photoconductive insulating layer in unexposed areas,

References Cited in the file of this patent UNITED STATES PATENTS 2,408,144 Huebner Sept. 24, 1946 12" Jacob Oct. 1', 1957 Grieg Oct. 29, 19.57 Mayer June 30, 1959 Metcalfe et a1." Oct. 6 1959 Herman Nov. 3, 1959 Rose Mar. 21, 1961 

14. THE METHOD OF SIMULTANEOUSLY DEVELOPING DURING EXPOSURE IN EXROGRAPHY COMPRISING POSITIONING CLOSE BUT SPACE FROM A UNIFORMLY CHARGED SURFACE OF A PHOTOCONDUCTIVE INSULTING LAYER ON A TRANSPARENT BACKING A DEVELOPER SUPPLY OF ELECTRICALLY CONDUCTIVE INK COMPRISING A HOMOGENEOUS LIQUID SOLUTION AT A RAISED ELECTRICAL BIAS POTENTIAL OF THE SAME POLARITY AS THE CHARGES ON THE SENSITIVE PHOTOCONDUCTIVE INSULTING LAYER AND AT A POTENTIAL ABOUT EQUAL TO THE POTENTIAL OF THE CHARGED PROTOCONDUCTIVE SURFACE, PROVIDING BETWEEN SAID SUPPLY AND SAID CHARGED PHOTOCONDUCTIVE SURFACE FLOW AIDING ELEMENTS IN PHYSICAL CONTACT WITH SAID INK AND SAID CHARGED SURFACE, SAID FLOW AIDING ELEMENTS BEING REGULARLY DISPRESSED AND SUBSTANTIALLY EVENLY DISTRIBUTED THROUGHOUT THE AREA OF CONTACT, EXPOSING SAID PHOTOCONDUCTIVE INSULATING LAYER THROUGH ITS TRANSPARENT BACKING TO A LIGHT IMAGE TO BE REPRODUCED, AND DURING EXPOSURE VARYING THE POTENTIAL APPLIED TO THE INK TO CAUSE THE BIAS APPLIED TO THE INK TO REMAIN ABOUT EQUAL TO THE LEVEL OF CHARGE IN THE PHOTOCONDUCTOR AT POINTS OF LIGHT EXPOSURE CAUSING INK DEPOSITION ON THE SURFACE OF SAID PHOTOCONDUCTIVE INSULATING LAYER IN UNEXPOSED AREAS. 